The answer to this question can be found in Chapter 6. Tom draws a house and a man. Although he draws them very badly, Becky Thatcher must be at least a little bit impressed. We can tell that she is impressed because later on, when Tom writes "I Love You" on his slate, she is not angry.
Tom drew the house first. Twain says that it was a pretty dismal effort at a house. But when Becky saw it, she said that it was quite nice and she asked Tom to draw a man as well. Twain says the man looked like a "derrick" and was big enough to step over the house, but Becky was impressed even so.