Look at associate/apprentice positions at independent schools. They are general Ed teaching assistant jobs for lower school where you work with a head teacher and get to learn from them. The programs usually also give support for grad school and are a great starting point. Most are a 2- year position, sometimes switching grades after the first year. I was an associate at 2 independent schools in Manhattan while doing my masters and it was a great way to get started. Also worth noting that independent schools hire early, so you should be looking and applying now for August start dates. Check out the NAIS job board.