Snap Circuits Upgrade Kits
With these kits from Elenco, you can start with the basic kits (see above) and add on without duplication. If you began with #28551, the 100 experiment kit, you can choose one of the upgrade kits like SC-100 to SC-300 with experiments 102-305, SC-100 to SC-500 with experiments 102-511, or SC-100 to SC-750 with experiments 102-692.
All right, so you've purchased the 300 experiment set, #29506, for your little science whiz and now you want to add to it. Depending on how much you want to add, you can choose from SC-300 to SC-500 with experiments 306-511, or go with a double upgrade set and include experiments 306-692.
If you have already purchased the 500 experiment set, #29507, the only set you'll need is SC-500 to SC-750 which includes experiments 512 to 692.
Each kit comes with all the parts and an instruction manual for completing the experiments. It is important to note that the kits are upgrades and aren't very useful independently. They are intended as add-ons to the basic kits and the parts contained therein.