My primary school students are confused by BODMAS and think that it only applies in certain situations.

I am guessing BODMAS stands for Brackets, (I don't know), Division, Multiplication, Addition, and Subtraction. In the U.S.A. we use PEMDAS. PEMDAS stands for parentheses, exponents, multiplication or division, addition or subtraction. Just because the A comes before the S in BODMAS doesn't mean always add before subtraction. To help them with this put the word "or" between the letters "D" and "M", and "A" and "S." Tell them that when you solve the problems in the brackets or parentheses, do the exponents or what the "O" stands for. Then, ask them to find the first multiplication or division problem from left to right and solve it. Next, find the other ones and solve them. Last, they do the same thing, but with addition and subtraction problems. I hope this helped.

I live in the US and we term it PEMDAS, but the principles are still the same......

1. Work  inside the brackets [parentheses], first

2. Perform any exponentiation, next

3. Perform any multiplications/divisions as we encounter them from left to right........this is the thing that usually gives people the most trouble.......many people think that multiplications are performed BEFORE divisions, but this is incorrect......for example:

10 / 2 * 5   =   10 / 10  =  1     [ incorrect ]

10 / 2 * 5   =   5 * 5  =  25   [ correct ]

4. Next, perform any additions / subtractions as we encounter them from left to right

BTW ...using (4) above.......   10 - 3 +  7    =   7 + 7     = 14  

I think you should firstly tell them that addition and subtraction are EQUALLY IMPORTANT 

They must be done from left to right.

ALSO

The minus sign is 'glued' to the 3.  They are in fact adding minus 3.  If the terms are rearranged the minus must always be in front of the 3

I really like it when teachers ask questions here. :))