Well the historical context is barely relevant unless it contributes to an analysis of Shakespeare's use of characterisation. Instead of recounting the play (both the text and the play is a socio-historical context) your son should be making a literary analysis of the text. He should identify and amylose the use of literary techniques such as characterisation, symbolism, poetic techniques (metaphors, imagery etc) incorporating quotes within the text.
For example, if he wanted to discuss the play within a historical context his broad theme would be Shakespeare's characterisation of Macbeth as a villain to satisfy his mobarch's dislike of the historical figure.
In his introductory paragraph he would make an opening statement e.g. Shakespeare's Macbeth was portrayed as (insert appropriate quote about his fiendishness) contrary to true historical events in the author's attempt to please his morach. Then he would make three Sen races briefly introducing the themes of his body paragraphs. E.g. The author utilises evocative imagery (insert a few quotes) to communicate the duplicity of Macbeth's actions contrasted to his true 'desires'. Then a closing statement such as: Masterfully utilising techniques a, b, c, Shakespeare crafts a complex and multidimensional Macbeth that, while far from the genuine article, nonetheless creates an authentic character.
In his three body paragraphs he should choose one technique per paragraph through which the author statistics his aim of creating this sinister Macbeth. For example he could use imagery (dark imagery is a strong theme is the play, stars hide your fires undoubtably one of the most evocative and memorable words ever written by a man is simultaneous heart breaking my beautiful and sinister). Another technique may be setting. The majority of the play's significant scenes take place in dark and sinister settings (the encounter with the witches, the murder). This can be cobrasted with the 'above board' daylight scenes to illustrate Macbeth's duplicity. Lastly he may choose to analyse supporting characters with a particular focus on the female characters throwing into relief Macbeth's inner turmoils again the contrast between male and female characters can show duplicity. Think witches=evil ambitions, lady Macbeth, a guilty conscience and the deeply dare anger nature of his acts.
Lastly he must have a covlyding paragraph of about three sentences where he restated broad theme, the techniques he has observed and general closing statement on their success.