Are you using baking powder (levure chimique)? If so, it may be stale--or, if you're adding a lot of acid juice (like orange juice) to the recipe, it can deactivate the baking powder. Another possibility is over-beating.
I have a super recipe. Weigh your eggs(3). Whatever the weight is use the same weight of margarine, sugar and flour(gateau flour). Cream fat and sugar, add eggs one by one, add flour and bobs your uncle you have a nice sponge. Cook at 180-200c. for about 20 minutes. The time may vary according to your oven. Good luck!
I sometimes over 'play' with my sponge cakes and that causes them to become very flat! Also I have found that keep opening the oven to check on them (which my kids love to do) does not help the rising process
Until i came out to live in France i could not make a sponge cake no matter what i tried,but since coming out here i have no problems,they are light and rise well,our French neighbours love them.I use the cheapest margarine,the cheapest gateaux flour and our own fresh eggs,works for me ,good luck with your baking.