Could you please help me with it?

Is there any grammatical mistake in it? Is there anything that is not natural English? What kind of problem do you see in it. Please help!

My First Experience of Teaching

Last year, I had to teach some first graders in a school, and I have a lot of good memories of it. It was my first experience of teaching, and I didn’t know anything about teaching children. Because I never taught children before. The first day of school was very boring. Because, I didn’t know what to do with them. When I was speaking, they didn’t listen to me – they were simply ignoring me. Having no experience, I just didn’t know what to do with them for the first two days. But, on the third day, another teacher named Zahra came along and told me to treat those students seriously. When I heard that, I found out that I have been a very kind teacher all long. Fortunately, on the fourth day, they asked me to teach another class of first graders. In my new class there were 13 students. They were very silent and polite; needless to say, I couldn’t be rude to those kinds of student. The first day of my new class was great. However, the second day was a complete disaster. The students were playing, with one another. When I was trying to teach, they avoided me. That, caused me to treat them seriously. Surprisingly, when I was serious, they were good students, and when I was not serious, they weren’t good students either. One day, the manager of school came to me and said to me, “your class is almost empty. You must have 10 more students.” She did send some 10 students into my class; unfortunately, they were so naughty and noisy. And I was just not happy with them. Fortunately, a month later, I could turn all of those naughty students into some very good and nice student. It was an unforgettable experience, full good memories.