I don’t know who was teaching you Rebecca but if you read the Book of Mormon you will see that the Nephites were righteous in the beginning, the Lamanites were not. Then later on, the Nephites became wicked and the Lamanites became righteous. And on the cycle goes throughout the entire book.
And that, although God chose to curse some wicked people by darkening their skin, He never stated that ALL wicked people will be cursed with dark skin, nor did He ever state that ALL dark skinned people are cursed. Never in the Bible nor the BOM will you find that passage.
But then you were in 2nd or 3rd grade. You might not have understood it properly.
Of course non-doctrinal teaching is discouraged. All teachers from Primary all the way to the Bishop are given guidance on what to teach. The first thing you get when you get a call to teach is the book, “Teaching, No Greater Call” and it is VERY clear in that book that a teacher cannot use materials that are not endorsed by the Church (such as the Journal of Discourses) and a teacher cannot use personal examples/personal anecdotes/stories that are not in-line with the material. In fact, all lessons are outlined in a lesson manual and one cannot deviate far from it. The presidencies are required to provide training to the teachers and the Stake hold teacher trainings as well.
I should know. I teach the 8 year olds.