The six lowest level books, in Set One, have no words in them, allowing reluctant and struggling readers with the greatest difficulties to engage with narratives. The Set One books are also valuable as starting points for discussion and creative work. Set Two introduces a very limited number of words on each page, with Sets Three and Four offering a further degree of progression.
In all cases the texts focus on high frequency vocabulary, with all words being phonically decodable wherever possible. The highest level Thunderbolts books have a reading level that is below that of the popular sister series Trailblazers series.
As with the Trailblazers series, these books combine a non-fiction section with a fiction story on the same topic.
All of the Thunderbolts reading books are supported by workbooks containing worksheets specific to each title, as well as detailed teacher's notes and advice on working with the resources. The workbook tasks are varied throughout, to allow a degree of progression as they are used.