Tense?

TJ was working on a homework assignment after dinner. He had a paper full of verbs in the present tense and he had to write down the word in past tense. Blow? Blew. Throw? Threw. Lead? Led. 

He was zipping right along. He was coming up with all of the answers on his own; he just wanted my assistance on the spelling every once in awhile. 

When he got to 'spend', he only hesitated for a second before he blurted out 'spought!' He immediately realized his error but not before we all had a good laugh. Bill said he should get extra credit for inventing a new word.