The score to beat for stage 1 is 214,500.
Stage 1 and Stage 3 were the hardest for me to beat "dad's score" (which I was able to do on Normal or higher on every other level), but here's how I finally accomplished it. I mainly used the spin-on-the-ground combo (A then X's) after waiting for as many zombies as possible to gather around me. I also had to do it on Easy, since they're easier to kill with that combo in Easy mode. Every time there were 3 or more zombies, I attemped this. The goal is as many sparkle hunting bonuses as possible throughout the level. It didn't always work, but it was enough to put me safely over the top when the end-level bonuses were added.
Beyond that, just do everything you can. Rescue the students, don't die/restart if you can help it (which you easily can, on easy), get all the QTE's, etc. Note that even if you manage to beat the score before finishing the level, the achievement doesn't unlock until you do, once the scoreboard appears and bonsuses/penalties are added.
I failed once at Basketball because I was trying to pad my score with zombie kills while another was blocking the basket and ended up not leaving myself enough time, but even so, my ending score was something like 60k more than I needed.
Good luck!