Have you ever learned something from school in the past that you’ve come to realize was incorrect?

Yes! In general, I realized a lot of the health advice (physical and mental) I learnt was wrong now that I am pursuing a science degree. A few examples: 

1. "Natural sugars are healthier for you." Not true. They are actually the same as unnatural sugars and your body cannot decipher the difference, it is only an ethical choice whether you prefer "natural" or unnatural. 

2. Same with vitamins. "Naturally sourced" vitamins of any kind are the exact same as ones synthesized in the lab in supplement form. 

3. Another example I remember learning is that 100% fruit juice is healthy for you. In fact, one cup of 100% fruit juice contains nearly the daily limit of sugar for average adult women (about 25g), and all the main healthy components of fruit are transferred into the juice.

4. Also, you don't need dairy at all yet they taught me that you needed a few servings of it a day. You can get all the calcium and vitamins and minerals found in dairy in fruits and vegetables. In fact, the vitamin D in milk is added and doesn't even occur naturally in milk. Plus the hormones in dairy can conflict with human hormones so it is not actually the best idea to have dairy every day. I still do because I like the taste and my body doesn't react to it, but a lot of other people are dairy sensitive and shouldn't have it.

5. You should "do what makes you happy." Studies actually show that at the end of your life, old people always claim that their happiness comes from quality relationships. Those who prioritized career, success, and their personal goals and aspirations over relationships reported feeling unhappy in the end, unless they achieved quality relationships alongside. So, it is actually equally important to do what makes others happy, at least those who matter to you, who you want to maintain relationship with. Living your life for yourself and neglecting the needs of those who matter to you will leave you empty. Sometimes you have to give up what makes you happy to keep harmony in your relationships and achieve life satisfaction in the end, like giving up your dream job in order to maintain a healthier "home life" for your family. On your deathbed, its your family you'll be thankful for, not your job or individual success. Humans were made for relationship, its what makes us happy. North American society preaches way too many individualistic messages that are straight-up recipes for depression.

Yes at school we called the Police Pigs got to Highschool and we were told that Insults the Pig so the Police became the Filth and here I am over 80 and Know it to be true

Of course. Even teachers aren't infallible.

"future du passé is the same as condictional" and "all languages have irregular verbs"  both aren't true

same goes for "creating money always causes inflation"

Yes, we gain advanced scientific knowledge all the time. That's why it's important to keep up by reading. 

not that i remember

Yes. Facts sometimes become outdated are wrong, especially scientific facts. History gets?rewritten within seconds these days. 

Yes, not only was it said or omitted in school literature about cigarettes being harmful, even after they realised they are bad for you, they changed it to cigars and pipes are healthier because you don't inhale but that is not true because it still goes in your blood and you're breathing it in between puffs.