He's a boy and sadly for you, boys tend to treat this test as being very dull. Maths questions have a set process to the correct answer - this normally provides boys with the satisfaction they're looking for. With English comprehension it's not so simple. The questions (and their answers) tend to be more subjective and answering them requires careful consideration.
First step - Boys like to scan-read the texts for facts in the hope of quickly answering the easy questions. If your boy is doing this then they need to stop, they're only giving away easy marks. Encourage them to read the whole text before reading the questions.
Next, when your child is reading the text, encourage them to write a summary of it - characters, plot, objects etc below it as they're reading it. This helps a bored child understand and 'take in' a dull story. They may also want to underline or somehow mark a point in a text with a key moment or change (i.e. a part where a question will likely arise).
Lastly, they need to practise. It's easier said than done but if they're poor in practice then they will likely be poor in the real test. Surprise results are very rare in this style of assessment (hence why it's used!)
To help motivate boys, I've always brought numbers into it. E.g. if they score 10/30, encourage them to beat that score next time. If a question has 2 marks, they need to find two points to make within it etc.
Best of luck!