Finding the hidden 4 letter word. It is always a 4 letter word, so will always be one of 3 combinations..
The last 3 of one word and 1 of the adjacent word.
The last 2 and the next 2
The last 1 and the next 3
Occasionally they will go over 3 words.
So teach your child to look for combinations of [3,1] [2,2] [1,3] He could use his thumbs/fingers/pencils to cover all other letters, so only 4 letters can be viewed. eg THIS LEOPARD. Thumbs would be covering TH and OPARD leaving in full view the word ISLE
If you are completing Multiple Choice papers, your son can work directly from the answer sheet, because the layout is such that the words are grouped in pairs.
FInding the missing letter for 4 words, if multiple choice look at the letters on the answer sheet, if he cannot see the words in his mind, get him to write the letters next to the part words, many children need this visual option.