Teachers gravitate towards private one-to-one lessons for a number of reasons.
They are financially lucrative if you take students privately. One school I worked at charged students 35€ for an hour and half lesson and paid me 23€. Working on my own, I could easily charge 30€ a lesson and both sides benefit – the student pays less and I make more. (Of course, I found students on my own, not by stealing them from the school.)
Students who take lessons are often interesting people. While part of a lesson will normally include grammar or vocabulary, at least some of it will involve talking and actually communicating with the student – a person who will likely have experiences and a worldview vastly different from your own. Often students are people you would never meet in your everyday lives . I’ve worked with a judge, an auto club president, two Hungarian sisters who grew up in the UK, and an economics professor.
Word of mouth or networking is probably the best way to find private students. Some people put up fliers at universities or English language bookstores or in other public places. Others advertise in newspapers. Potential students may approach native speakers on their own; I was chatting with a classmate on the tram during my TEFL course, and a woman approached us and asked if we gave private lessons, simply because she had overheard us speaking English.
However, taking on private – or relying on them to make up the bulk of your income – can be risky as well.
Many schools ask their full-time teachers not to teach private students – they want the time and energy (and their materials and photocopiers) used for their students. And certainly they don’t appreciate teachers who take the school’s clients and teach them privately. Schools are likely to find out if you are violating terms of your contract, and even if they don’t, they may ask you to teach at a time when you have a private lesson arranged.
Students cancel private lessons all the time They go on holiday or just take breaks for undetermined amounts of time. Highly motivated people who genuinely want to take classes may put off calling you for a month. Many schools have 24-hour policies; if students cancel with less than 24 hours notice, they are still billed for the class. You can ask students to give you notice if they cancel, but enforcing this policy on your own is extremely difficult.
You have to provide materials for private students. “Conversation” may work for several lessons, but after some time you will need something to base that conversation on. You also often have to travel to their premises which may be time consuming. You have to arrange work permits/residency on your own, which is often very difficult, expensive, or even impossible without a regular employer.
Given all of these considerations, teaching private students can be a lucrative way to supplement your income and an interesting way to spend some of your free time and earn money at the same time.