I have not heard of this before, but is probably means that the students ask friends/relatives to promise to donate a certain amount of money for each word they spell correctly at a spelling bee, which is a spelling competition for kids. In America, we use similar approaches to raise money. For example, there could be a charity wallk-a-than (long distance walk) in which people get friends/relatives to agree to donate $1 per mile for each mile the person walks.