I'm working on an educational product, and we're thinking of introducing some gamified aspects to motivate students to use the product. One of these will be the concept of 'levels' - when a student does enough lessons in a particular topic, their 'level' in that topic will increase.
Is there any kind of research on how to best space these 'levels' out in order to maximise motivation? If students can progress through levels too quickly then leveling up will be devalued, but if it takes too long to get through levels then they may be less motivated because the end won't be in sight. How long should we aim for students to take to get through a level? 1 week? 1 month? 1 year?
Any advice on how to approach this problem would be greatly appreciated.