As, being told you tried things like different markers, repeating basic exercises, etc. To me, it seems like, maybe the child has feared fora fear of mathematics. We can help him out by working ininnovating the following manner :teaching methods. For example,
1. Make the class interesting, with objects, presentations
I used the image pinned below for preassessment class to know how much my children are interested in particular subjects and thingsSome theme-based presentations designed with contents focussing on logic development can help. What I gotThis may also engage a child to know was children learn things quickly when they are taught with some new ideas/activitiessolve a problem interestingly.
So, with an example of two friends having 5-5 berries, we can help him to deal with numbers easily! like if friend 1 is supposed to give 7 berries to another friend he has to borrow 2 berries,i.e,-2.
2. Introducing to topics in a new way!
We can simply introduce him to the topics by telling him that the topic we'll be studying now is one of the easiest in Mathematics. We can give exposure to a topic to a child with the help of real-world examples/applications, or by conducting some fun activityactivities. Introducing topics in such a manner willcan work in two ways: first, the students willwould be eager to learn the topics and attend further classes. Second, they'll understand why the topic is being introduced.