Aryan, Zain, Nilukshan, Gharan, Sajuthan, Ibraheem, Tianah and Salome from Northgate Primary in the UK focused on how to find the headings having revealed the answers.
This is the beginning of Sajuthan and Ibraheem's work:
 

Aryan and Zain focused on the signs of the numbers in the answer:
 
If in the [product] the top digit is negative (e.g. $-5$ and the bottom is positive (e.g. $+6$) both numbers that make the [product] are negative.


Nilukshan and Gharan continued this idea:
We found H.C.F. out of the 4 numbers (in this case, the bottom numbers, $+6$) in each row. Then we found if the H.C.F. would be positive or negative. After that we put the negative or positive number on the box of the row.


Tianah and Salome described how to find the two factors from the answer. This is their work. Read down and then across.
 

Tanya from Bangkok Patana School in Thailand thought about how many answers you have to reveal in order to find the solution. This is Tanya's work:
 

It is actually possible to do it by revealing $2(a-1)$ answers: