 If you liked Charlotte |  ...then you might like Youkoso Jitsuryoku Shijou Shugi no Kyoushitsu e |
The main characters are very same. Their relationship is very similar. Both are school drama with similar vibes. If you liked one you will like other for sure.
Both stories are, of course, set in high school but there's more than that. The main characters share experiences: making new friends in a brand new school, adventures to find a truth or build a relationship, and a good opening... Both shows also focus on a 'minority' group of students (geniuses? in Youkoso and kids w/powers in Charlotte). Also, I watched them each in 3 days... what am I doing with my life...