I explained 2 strike hitting to my kid when he was 10. Took 6 months for him to improve the skill enough you could see he had it and would continue to improve over time.
At 11 I told him to go to the box and hit like it was 2-0 on the first pitch. Pay attention from the first pitch from the dugout for what the pitcher liked to do and zone in on the pitch. If he liked to throw FB away...go up there and look for it. If you get what you want bang it. If not take it. If it is a ball hit like 3-0. Zone it down to a specific pitch and spot and take if it isn't what you want. If it was a strike...continue to hit like 2-0 until 2 strikes and then shorten up.
At 11 to13 years old he would have stretches where he would just kill whoever was out there. He would have weekends where he would get 20+/- AB's and hit 18 hard. His approach was superior to almost everyone at his level. He also had the most important piece which was the ability to adjust in game. If you got him on a change or curve on the first trip, he'd look for it on the 2nd and nail it.
In HS he faced about 3 pitchers that he had to be less aggressive with because they actually had plus fastballs and a breaking ball they could throw for a strike. At that point he was hitting FB and adjusting to the breaker down in the count.
This approach works only if two things are present. A batter that has the skill and confidence to be able to make good contact with a shortened 2 strike approach and a coach that does not lose their mind if a player takes a fastball strike...especially on the first pitch of the AB.
For probably 75%+ of HS hitters...first ball - fast ball is a sound approach. For the others this will work. Every kid I ever encountered if they were smart enough to get this approach was a tougher out then they were before and those with the talent were VERY tough outs all through HS.