What would be a great product to sell to educators, particularly school teachers?

I think it needs to search for those topics related to each educational institution

I believe every school or a chain of school has its own needs and wants. The best way to market things to teachers or to school is to conduct a series of survey. That you can conduct online, via email, via letters etc...... And believe, you will find surprising facts. 

Well it depends! everyone has different opinions and perhaps different schools (and across citifies) have different needs. You are now getting in "New product development". The best way to find out is surely by asking the teachers themselves through (focus groups) or (interviews) or by simply observing what are their pain points, Great products come up from great observations. Sometimes customers have difficulties and troubles but don't understand it or even got used to it. So, coming u with a product that blows their mind and make their life easier will surely will be quickly accepted.

Hope this helped you out :)