Mathematics is an interesting subject and the beauty about mathematics is that you can score 100% in Mathematics if all your answers are correct. When compared to other subjects like economics, social science, the history we do loos marks and its not always you get 100% in other subjects when compared to mathematics. Now coming to your question about building the interest in mathematics in secondary school than I would like to share my experience here as to what our school did to develop interest amongst the students.
1- Mathematics with fun - it drills down to the teacher teaching the subject. If we have a teacher which teaches the subject in a fun learning manner that we would see students who fear maths would also start taking an interest. Back in my schools days, we had a teacher who used to give real-life examples and made the subject interesting and once a subject is made interesting we see mass adoption.
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2- No enforcement or pressure - it is a tendency when you enforce things people try to run away from it. Applying the same analogy if you enforce than let me assure you that it won't work. We need to create interest first by giving demos, real-life examples show students the great benefits that Mathematics has in itself - and as a result, you will see the acceptance ratio increase. Enforcement doesn't work at all. Just take out that fear in a student that mathematics is difficult and you will see the positive outcome.
3- Organize competitions - In our school we had mathematics competitions for all the classes. Competitions lead to building that interest in a student so that he can change his or her perspective on the subject. Also, when they see that their mates can do it that why not they themselves - it creates that interest of winning and as a result, we see mass adoption of students gaining interest in the subject.
The above-listed points:- Fun learning, No enforcement and organizing competitions really worked out well in our school and saw a lot of students really take interest in Mathematics subject instead of fearing it and bunking the classes.
Interesting subject. From my experience as mathematics teacher, I discovered students are not as bad in mathematics as their grades suggest. They are mostly lazy mentally. They have created a kind of blockade even before listening to explanations.
The first thing is your students have to like you first before they like mathematics or whatever subject you are teaching. From a teacher's first day in class, (S)he must have a way of breaking the teacher/student wall. It will be easier to students to listen to your every single words once you develop a connection.
While it can be hard in some topics, using examples and description students are familiar with helps. For example, you can number of boys/number of girls against total number in class when explaining probability or pocket money to explain word problem. They can relate to these example and it makes the class interesting.
Create friendly competition. The most memorable class I had with the students was when I created a competition. This competitive atmosphere led to a lot of fun even for the final year students, and me. It was like they all wanted to prove how intelligent they are. Giving a small gift to the winner(s) add to the effect on them.
I hope those points help.