Not getting credit for strengthening skills
Today I've had three skills that I strengthened and nothing changed on their status. Education was one of them. It was rated 4/5 so I took the quiz and got 19/20 correct. Afterwards it was still 4/5. If it doesn't recognize improvement, why bother?
The strength of a skill is based on the average strength of each of the words in that skill. I think that the selection of words is made randomly so you may not have strengthened sufficient words to get you into the Gold range.
It's a quirk of the way the skill strengthening works--this isn't the best explanation, but it might help you understand. It might also just mean that you need to strengthen the skills a few more times before the skill gets re-gilded.