I really liked this. It’s simple, but it’s very reminiscent of a typical, believable childhood experience. Most of us were Eddie, at one point or another.
– I’d rework the opening. The first sentence is long and throws too many details at the reader. I’d cut it and make the second sentence the first, then scatter the setting details around the rest of the story.
– There are some passive-voice verbs that could be easily rephrased into active sentences (for example, the sentence about Eddie discarding his homework), so I’d rephrase those.
– I’d replace vague, subjective terms (like “gaudy” and “tacky”) with more specific descriptors.
– Eddie should have stronger motivation to avoid telling his mother about the incident—the Nintendo, perhaps. Maybe he suspects she’s saving up money to buy one for him for his birthday because he found a cut-out advertisement in the drawer of her nightstand. Maybe he also believes the knocker could be older neighbor kids who bully him on the bus, so he doesn’t want to say anything and risk looking like a baby. (This would also explain why the knocker can call his phone, and how they can access the door so quickly afterward.)
– The system Eddie and his mother use to verify she’s calling is inefficient. (I’d be interested to know if other people used this system.) My mom allowed me to pick up the phone but didn’t allow me to respond. The other party had to say, “Hello” first. I’d recommend another method than this 1, 2, 3-ring system.
– I like the idea of the conclusion more than the execution. I’d personally prefer for the identity of the knocker to be more ambiguous. If the knocker entered the house, why would he waste time writing on the paper when he could be finding Eddie? And how did his mother not see the homework/note when she entered the house? Wouldn’t she have noticed the unlocked door? I would like to see a more satisfying climax and conclusion.