Reliability
On the other hand, school inspectors had their own agenda and it is always worth asking why people write as they do, even in official documents like these. If you look at the end of the source, you will see that the Inspector is making some quite specific recommendations to his masters. These are designed to influence policy and the cautious reader might like to think about whether Tremenheere's statement is necessarily giving a full and accurate picture.
'Where, to use a modern phrase, is he coming from?'
For example, is there likely to be any 'spin', designed to convince his employers of the need for further action? Is he proposing this because he genuinely believes that the measures he advocates are necessary, or because he wants the job of education inspectors to be made more manageable? As with so many enquiries in history, there is no definitive answer to this, but it is necessary to try to understand things from the perspective of the author. Where, to use a modern phrase, is he coming from?
Tremenheere is a bureaucrat. He likes tidy solutions. We should perhaps balance his comments on what he sees as the shortcomings of the Whitehaven union against more detailed knowledge about the local situation.
There might have been good reasons why the school attendance officer had not made more visits, and the union's policy might have been influenced by a more thorough knowledge of local conditions than a government inspector could obtain on one visit, however detailed his enquiries. So, it's worth asking whether Tremenheere is making critical judgements on the basis of insufficient detailed evidence.