My son Satyendra who is now studying in class 10th, was struggling in Maths and Science till last year. At that time one of my office colleagues told me about this wonderful website-Meritnation.com. From the time that my son has started studying Maths & Science from this website, he is able to clear all his doubts quickly with the help of online videos and he was able to score an A1 in both these subjects in class 9th.
Test Generator by Meritnation is the feature that I personally like the most. Using Test Generator, you can choose chapters and create as many tests that you want for practice. In addition the website also has study material, tests, videos & animations that are very useful.
I believe that this is the best website for 1st to 12th students.