Decide what 'it worked' means BEFORE you start

Pinpoint

[worked example] My 3yo hits her baby brother when I'm feeding him — about 3-4 times a day.

Your best guess at why

reward

The ONE thing you'll change

Give her a specific job during feeds (turn the book pages, pick the next song) so she gets attention for helping instead of for hitting.

Success looks like

Hits drop from 3-4/day to 1 or fewer/day within 10 days, tallied on the fridge; zero is not the bar, fewer is.