Jean Sibelius's career as a teacher began in Loviisa in the autumn of 1891, when he put an advertisement in the newspaper and began to teach a few pupils.

At this stage Sibelius was regarded as one of the most promising Finnish composers. The people of Loviisa were aware of his skills as a violinist and of his studies in Berlin and Vienna. Sibelius managed to earn a small amount of money by teaching violin playing and music theory. Indeed, there were a couple of months when he had enough pupils for a small pupils' orchestra.

His teaching ended in January 1892 at the latest, when he moved to Helsinki. In the spring of that year he was fully occupied with putting the finishing touches to Kullervo, and in the summer with the wedding arrangements and the honeymoon.

In the autumn of 1892 Jean and Aino Sibelius set up house in Helsinki. Sibelius had obtained positions both at the Music Institute and at Kajanus's Orchestra School. Sibelius taught violin playing and musical theory for a very small remuneration. Sometimes he had over 30 hours of teaching in a week. The pupils were a mixed bunch. To some of them he only taught elementary theory, but with Otto Kotilainen and Axel Törnudd he could quickly advance further. Kotilainen later had a detailed recollection of Sibelius as a teacher:

"Of course it would be wrong to say that he did not care about rules, but he was not at all in favour of following them too strictly. If the melodic and harmonic progressions sounded good and if the exercise as a whole made a good impression, he often just mentioned the rules briefly and at the same time acknowledged the student's taste. 'I myself have been forced to struggle with strict rules,' he once said during a lesson. 

"So there we were, slaving away, going back and forth through M. Wegelius's Musical Theory and Analysis I with its scales, intervals, harmonies, unfamiliar progressions, not much text but plenty of examples of everything. We listened to the overtones [harmonics] of various notes. He would throw open the lid of the grand piano, step on the pedal the and hit a low note. And then we listened, all eyes and ears. 'Sometimes when I've been in the countryside,' my teacher [Sibelius] said, 'I've heard the overtones in a rye field while I've been lying down in the grass.' I nodded to assure him that I believed him. 

"He also had time to deal with instruments during that lesson. For example he asked: 'Do you play the flute?' and when I answered in the negative, he continued: 'It lies - and the higher it goes the more it lies. 'Flöitaa [= to lie]. That's how it got its name.' And I believed him. 

"My teacher walked around for a while, smoking. 'Have you written any continuo?' 'Yes I have - on my own', I answered. And as I had the book with me, he ticked several exercises from different chapters, asked me to do them, slipped away himself and even went into town for a while. He returned about an hour later and I had done almost all the exercises by then. He looked at them with a frown. In some places he wrote something to show that a certain sequence would go better in such-and-such a way, but that another way was also correct.

"I've described the occasion above at length - it lasted almost three hours in all - because in a way it was my entrance examination to be Sibelius's student. It was a real whirlwind of theory, and after that we did not discuss general musical theory at all as an actual subject. While the ladies were sweating with the basics I quietly started to write out harmonies and later actual counterpoint, which I continued to do when I moved to study at the Orchestra School, along with my teacher. This was because I had passed what were regarded as compulsory subjects at the Music Institute. At the Orchestra School I began to experiment with composition, as well as harmony and counterpoint. I first tried choral and solo songs, and later small pieces for orchestra. Throughout this period, several years actually, Jean Sibelius was my teacher. The memory of those lessons still puts me in a warm and happy mood. He was able to give so much inspiration and encouragement to me, his pupil. And when I showed him my compositions, his comments and advice always hit the nail on the head. He never used an instrument, he just read what I had written - with those familiar furrows on his forehead - and when he came to the end, he pointed out the weak point which had to be changed for next time."

At the Orchestra School one of Sibelius's pupils was Axel Törnudd, who started his second year of study in the autumn of 1892. Törnudd's recollections of Sibelius as a teacher are equally impressive:

"His constant advice was: 'Make your compositions simple! The simpler, the better. Look at Palestrina, how he is so transparent and clear! I myself strive with all my might for the greatest simplicity.'

"These were strange words from the mouth of the composer of Kullervo! The master of chaos preaching transparency and simplicity! I must confess that I sometimes laughed in my beard (although I did not have a beard), when I thought about the advice and who was giving it. I did not for a moment doubt the master's deep sincerity when he said that, but I wondered how this Titan, who had so much passionate blood in his veins, could be striving for that kind of simple clarity. And for many years I continued to wonder."

Sibelius's burden of teaching actually increased in 1894, when he was briefly appointed to teach music at the University of Helsinki as a substitute for Richard Faltin. As Faltin grew older Sibelius and Kajanus obtained an increasing number of these locum posts. During this period Sibelius quite often applied for leave from his other teaching posts. In 1896 Sibelius finally applied for the post as Faltin's successor and gave a trial lecture, on folk music and its impact on the art of music. He was chosen for the post in the spring of 1897, despite the fact that Kajanus and Ilmari Krohn also had applied for the post. Robert Kajanus filed a complaint and was able to get the decision reversed. The complaint came as a shock to Sibelius, and after this he was always suspicious of Kajanus, whom he had regarded as a friend. Nevertheless, he continued to speak favourably of Kajanus in public.

Towards the end of the 1897 the Tsar approved of an annual arts grant of 3,000 marks (about 9,000-11,000 euros per year in today’s money) to be granted to Sibelius for a period of ten years. Later, Sibelius came to believe that Kajanus had fixed the grant for him, as compensation for taking the post as music teacher at the university.

The grant was about half of a professor's salary. During the first ten-year period it equalled about 11,000 euros in today's money. The grant did not solve Sibelius’s economic problems, and he was still teaching as the 19th century drew to a close. During the years 1899-1900 he occasionally gave lessons at his home in Kerava, as Otto Kotilainen later recollected:

"I often visited the master at his home, in addition to the lessons he gave at the Orchestra School. From these extra lessons I remember especially the times when Sibelius's family was living in Mattila House, near Kerava Station, and I travelled there almost weekly throughout the winter season. There the master usually sat at his desk, surrounded by thick cigar smoke, working on his creations, with sheets from scores lying all mixed up on - and probably even under - the desk. But I never noticed any expression or hint that I had arrived at an inappropriate hour; he always welcomed me and interrupted his own work (...) I had written a few small pieces for string orchestra, some of which had been performed at the public performances of the Orchestra School. My teacher advised me in his usual encouraging way to test my strength with a bigger work for full orchestra. 'Just jump into the lake and you'll have to learn to swim,' he said."

Sibelius still had connections with the Orchestra School circle in 1903, when his friend Axel Carpelan was trying to persuade him to move house as quickly as possible, away from the temptations of city life. In Carpelan's opinion, the income from the Orchestra School was of little importance, since the composer was already taking so much unpaid leave from his teaching duties. Indeed, the construction of Ainola almost completely interrupted Sibelius's teaching activity for a year or two.

On 22nd March 1906 Sibelius's former teacher Martin Wegelius died, and Armas Järnefelt was called on to take charge of the Music Institute. He persuaded Sibelius to return to the Institute as a teacher of theory and composition in the autumn of that year. Sibelius's most important students there included Toivo Kuula, who wrote an excellent piano trio under the direction of Sibelius in the spring of 1908, and Leevi Madetoja, who became Sibelius's student in the autumn of 1908. According to Madetoja, Sibelius started his first lesson (at Ainola) by saying that he was "a bad teacher".

"Well, who is a bad teacher and who is good teacher?" Madetoja said later. "In most cases it depends on the amount of interaction between the teacher and the student. And I have to say that already my first short visit to my master provided me with a great deal. It was not teaching in a narrow pedagogical sense. Only brief, cogent remarks."

This teaching period faded out, although Sibelius did continue to help Madetoja. Nevertheless, as late as the spring of 1916 Sibelius took Bengt von Törne on as a private student. "You do understand that I don't teach in the literal sense of the word and that I cannot give you ordinary lessons," Sibelius reminded him. "Moreover, I don't know whether I am a good teacher or not; I think that the better a person is as a composer, the worse he is as a teacher. In any case, I might give you some tips which you won't see in books on orchestral instrumentation, and in addition I can tell you some secrets I have learned during my long experience."

Bengt von Törne recollected his lessons in great detail in his short book, Sibelius: A Close-up. According to the book Sibelius emphasised to von Törne that there must be no breaks in orchestral instrumentation. He said that he preferred the "pedal effect" in moving from one tone-colour group to another. "I always add some of the second violins or violas to the middle range, which has no characteristic tone colour. You actually only hear the wind instruments, but the tone continues all the same."

The teacher also knew how to encourage his pupil. "So far your scores have borne too great a resemblance to Schubert's piano style. It is a common mistake in the first experiments of young composers. But this is different; in this score there are open spaces, and one can feel how fresh air is streaming in through the window. This time you have given it life and opened up clear views on both sides," he said during one lesson.

Sibelius did not want to teach von Törne for more than a few months. He was aware that a teacher with a strong personality can smother a student's independence.

After von Törne, Sibelius encouraged and advised many composers, but it is not known whether he gave any actual teaching lessons after 1916. He used to repeat a few key phrases over the decades: during the 1940s, when a radio interviewer asked him if he had any advice for young composers, he said what he had said to Madetoja in the autumn of 1908: no unnecessary notes; every note must live.

As a teacher Sibelius did not establish a school like Arnold Schoenberg, and he made no effort to create one. There are certainly Sibelian influences in Leevi Madetoja's output, but the main features in the portrait of Sibelius as a teacher seem to be spontaneity, and a gift to inspire. Sibelius seems to have taken his model of what a teacher should be from Karl Goldmark, his teacher during his year in Vienna, rather than from a stern drill-master such as Albert Becker, who gave him lessons in Berlin.

As a teacher Sibelius was at his best when the student could already compose and only needed the advice of a more experienced pair of eyes. His teaching techniques were not suitable for elementary drilling, but he could plant an ardent spirit of artistic honesty in his students.