That's odd. Probably a silly question, but are you certain that the sims you are trying to use this function aren't already maxed out on the skills you wanted them to learn by tabcast? Might you have any mods that could be interfering?
Where you said that your other store content is working, note that I was specifically talking about premium store content...but then I neglected to define what that means. That would be other content that has some useful newly defined functions, as opposed to say a piece of furniture, CAS parts, or even a regular appliance, plumbing fixture, or electronic that has just been restyled. That still leaves quite a long list, but examples would include basketball hoops, soccer courts, pizza/bakery ovens, baby dragons, zen massage tables, spell books, ice cream makers, etc.
Anyway, one thing that can cause premium store content to malfunction is a damaged ccmerged file. This is a small file that lives in the DCBackup Folder. It is possible to rebuild it by reinstalling ALL of one's premium content, but it's usually much easier to replace it with one that is known to work. This sounds like "cheating," but it isn't really as the content won't work at all if it hasn't been purchased for use by the account playing the game and ccmerged does not change that.
https://nonasims.wordpress.com/2012/05/17/dcbackup-ccmerged-package-and-your-premium-content-items/