Adding FTSE 250 (INDEXFTSE: MCX) growth stocks to an ISA could be a good long-term strategy, explains Edward Sheldon. : An allocation to FTSE 250 stocks within an ISA is a good idea, in my opinion, as the index is home to a number of companies that are growing quickly, and generating big gains for investors. With that in mind, here?s a look at two growth stocks within the index that I like the look of right now.