Honestly, there is no one single right way to go about this. The truth is, pretty much any school fundraising activity can be a success if you organize it with the right things in mind, such as the size of your group and your monetary goals. For instance, if you are in charge of a small group of school fundraising participants, it probably isn't the best idea to select a fundraiser with large minimum order requirements or shipping charges that will significantly dock your profits. Also, you need to keep in mind who the intended customer base is with your fundraiser.
If the kids are most likely to be selling to their fellow students, a direct sale product like chocolate bars can work really well, especially if you can arrange permission for them to sell the chocolate on school grounds. There aren't many kids out there who wouldn't go for a chocolate bar after lunch or after school, and with the price set at $1 a bar, this is a school fundraising activity that's affordable as well as fun. Schools can do very well with a candy fundraiser if the customers are also kids.
If you expect that the main buyers will be parents or families of the students, perhaps something like a catalogue fundraiser would be more appropriate - it just takes a little bit of common sense to figure out which school fundraising activity would be best for you and your group. We have all sorts of school fundraising activities, so be sure to browse through our school fundraising pages and see what might suit your needs.