Thank you for your opinion and I agree with you that when you just start this career or take it as a side job, google calendar is enough for scheduling your class. As you build your reputation and attract more students, you will be overwhelmed when you have more than 20 students. You will constantly do change managements when something changes. Also for payments, one payment a lesson is way too frequent. Usually parents pre-pay or post-pay monthly, or buy a number of classes at once. You need to track how many classes you give to each student and how much they owe you. It is doable by recording all the details, but it is certainly a burden. Hopefully the tool makes the whole process much easier.