Maybe. The absolute defense to a claim of slander is "truth." Remember, though, that whether statements are slanderous or not, the cost to defend such an action could be high. Be careful.
My answer is for general purposes only and is not not intended to establish an attorney-client relationship, nor is it advice upon which you should act or rely. But, if you really want me to tell you something upon which you can actually rely: don't eat yellow snow.
Sued by whom? I doubt the school will sue you. If you do get sued, truth is a complete defense. Your blog posts may constitue opinion depending on what you said and opinion is not actionable.
I am a former federal and State prosecutor and have been doing criminal defense work for over 16 years. I was named to the Super Lawyers list as one of the top attorneys in New York for 2012 and 2013. No more than 5 percent of the lawyers in the state are selected by Super Lawyers. Martindale-Hubbell has given me its highest rating - AV Preeminent - in the areas of Criminal Law, Personal Injury, and Litigation. According to Martindale-Hubbell”AV Preeminent is a significant rating accomplishment - a testament to the fact that a lawyer's peers rank him or her at the highest level of professional excellence." Fewer than 8% of attorneys achieve an AV Preeminent rating. I also have the highest ranking – “superb” – on Avvo. Feel free to check out my web site and contact me. The above answer, and any follow up comments or emails is for informational purposes only and not meant as legal advice.
Not knowing what you blogged renders a precise answer impossible. But if you mention one with specificity sufficient to identify the person, and the matter is incorrect and harmful, then you could be sued for defamation/libel. This is an analysis that should have been done before posting.
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My response is for educational purposes and does not constitute legal advice nor creates an attorney client relationship which requires all the details and a personal conference.