Physics is not putting numbers into memorised equations
Physics Narrative for 14-16
Teach physics – not algebra
The physics relied on in the arguments here depends on thinking about the flows resulting from the resistors impeding the flow of charge and the batteries driving the flow of charge.
This understanding is very physical: the effectiveness of the rope model exploits these relationships. Children are more likely to develop a feel for how current, voltage and resistance interact in a circuit if they are both challenged to think in these physical terms and shown how to think in this way.
To understand circuits is to imagine, without pain, how the currents and potential differences will behave. The currents and potential differences are seen to behave according to their characters. Being able to get inside these is the key to making friends with circuits.
Don't rely on memorised rules and algebraic tricks to jump to an analysis of a circuit. These shortcuts are for experts, not for beginners. Keep all reasoning as physical as possible.
Reason physically – use algebraic relationships only where these support this physical reasoning.