Class 8 maths marks dropped. Tuition now or wait for the next unit test?

Son is in class 8, CBSE. Mid-term maths came back about 20 marks below his usual. He says the algebra chapters went too fast and he didn't ask his doubts in class. Do we start a tuition now, or give it till the next unit test and see? Not keen on beginning something in class 8 that becomes permanent by class 10.