Kanji by grade. You learn the English and it also tests on the On and Kun readings.
Tests are also done in reverse for forward and backwards remembering.
UPDATES HAVE BEEN MADE TO COURSE, ADDITIONS, AS WELL AS CORRECTIONS, SOME ARE ONGOING AS THEY WILL TAKE TIME. MOST OF ON READING IS NOW IN KATAKANA AS WELL, THIS IS NOT AN ERROR.
Will add more grades as I myself progress.