From a teacher's perspective, it really depends on the goal of the student. If a student has a specific question in mind and only wants to focus on that, then potentially 30 minutes is adequate. Also, for conversation practice, 30 minutes is enough time to have a conversation and therefore get in some useful language practice. Perhaps shorter lessons are also better suited to children or those with shorter attention spans. However, if a student needs to develop their abilities across a range of skills and wants to work towards a bigger goal, then longer lessons are always advisable in my opinion. A new grammar point, for example, requires the introduction of the form and the uses, as well as then practice which is not possible to do adequately in a short time period.

It really depends on what you want from a lesson, how much time you have available and what the teacher is like. I personally would like to see more 45 minute lessons as I think this is an ideal length! I teach 30, 45 and 60 minute lessons depending on the student and the type of lesson. 30 minutes is ideal for practising IELTS speaking exams.

As a teacher, I would say that it depends on the student's language goals. 30 minutes is an adequate amount of time to go over some simple material, or to discuss a specific topic. It is also a great amount of time to have a conversational lesson. For more in-depth discussions, I suggest taking advantage of longer lessons. 45 minutes or 60 minutes is fine.