With an iPad, you should not have major difficulties accessing our learning environment and proceeding through the majority of our course catalog. However, the sizing may be a bit off.
Please note that some courses may request you download additional programs. This would mostly be for projects within our Paths. As you cannot download code editors to your iPad, this might present issues.
To supplement your learning we've released a mobile app called Codecademy Go! It's available in the App Store and Google Play.