How to effectively market conferences

For the past several years, I presented a school bullying/violence prevention conference to k-12 educators across the USA. I would contract with a hotel venue renting a meeting room to seat 30 to 40 educators classroom style. I advertised by sending emails to educators in the targeted area, submitting the conference to online directories, and emailing press releases to the local media. Using this advertising approach, filling seats has been a hit or miss. As of late, I tried running a Facebook ad with limited to no success. Because of school email spam filters and educators possibly discarding the email as spam, I am finding email marketing to be less effective. I am currently searching for a different and more effective form of advertising. Does anyone having any suggestions as to how I could effectively market to k-12 educators? Thanks.

Try contacting the Parent Teacher Association. Parents are more likely to be on board with this and have the funds to pay for their teachers to attend these. You can easily find contact information for the PTA group with a simple Google search.

Massmediapr kind of sites get the word out for that kind of event

Target Teaching associations and Teacher/Educational websites.
Probably more effective to contact the local school district rather than individual teachers.

Thank you so much for all of your recommendations. I honestly haven't considered any of these things. Perhaps these ideas will work. I considered the direct mail route. But given the low response rate for direct mail, I simply don't have the money to spend on it and keep the conference fee low for schools to afford. This is quite a dilemma.