There was a programme where primary-school kids were taught Esperanto as their first foreign language for a year, before switching to French for N years. Not on

There was a programme where primary-school kids were taught Esperanto as their first foreign language for a year, before switching to French for N years. Not only did those in the programme speak better French at the end than those who had learnt French for the whole N+1 years (which was the hypothesis being tested) but it was also found that many of the kids translated arithmetic problems into Esperanto before solving them and translating the answers back into English.