Writing testimony and/or public comment is easy because you are the expert! You don't have to be an expert on school finance by any means, but you are the expert on how legislation will affect your students and your school. That is an important voice in the process that is often left out.
During each meeting, for every bill that is heard, there is an opportunity to speak in support, opposition, or neutral. If you speak in support, you support the measure as is, without any additional changes. If you speak in opposition, you either oppose the bill in its entirety or have suggested changes (ie. amendments). If you speak in neutral, you are somewhere in the middle, but if the bill were passed as is, you neither support nor oppose it.
At the end of each meeting (sometimes this is done before and after), there is a period of public comment. This period is to allow the public to speak on issues that may not have been listed on the agenda. This is a great opportunity for educators to speak on a host of issues that may or may not be related to issues in the hearing.
With many campaigns, NSEA has letter-writing actions (i.e. Email the Senators, and tell them to x, y, and z...). The letter you write can serve as a great shell for public comment or testimony. No need to start from scratch! Many members use the letter they wrote previously and simply read it onto the record. It's a great way to double up advocacy efforts as well!