It can't be onsite because you don't have PHP/MySQL etc.
But it can't be offsite because you can't guard against who reads the posts, etc.
That's going to be sort of tough to do.
You didn't mention your age (adult or youth), but if the school
project was important enough, I would spend a mere $30 to get
a webhost account that HAS all of the scripting features you need, including
a WordPress blog, Joomla, or whatever else you need. That's pretty cheap!
Even x10hosting might be an option. That one is free and they offer PHP.
(not sure of the limitations though):