I'm new here, so I'm not sure if this is what you are looking for - but my son loves
www.ixl.com - it's math curriculum sectioned by either grade or skill - it does cost money but its only $75 a year I believe, and that's not too bad. The site goes from PreK to 8th grade, plus geometry and algebra, and the nice thing (for us anyway, and I'm assuming other gifted kids might be the same) is that you can bounce around to whatever skills/grade you feel like (we hover around 3rd grade, with a few dips into 2nd and random jumps into 4th-6th...it depends on the particular skill and my son's interest at the moment - It's good not to be pigeon-holed into a particular grade). They email weekly reports on progress and there are little "rewards" for completing particular skills, or working for an hour or whatever else (its just a big chart with stars that you can uncover to find fun little pictures...not much of a reward really, but my son gets excited about seeing a 'penguin' or a 'shoe' or whatever else is under the star - then again, he's 3 so I don't know how a first grader would like that part, lol.) either way, we have really found ixl super helpful, so I thought I would pass the info along
