Word Families originated from a large SMART Notebook file that I wrote several years ago, called "Handwriting Practice." It was designed to allow a student to trace over dashed letters to practice their handwriting. This Notebook file was never published, because an interactive whiteboard is a poor platform for teaching proper wrist placement and hand grip as part of handwriting skill development.
When I wrote "Handwriting Practice" I organized the words based on word endings, with one group of pages being -ack words, like back, black, crack, jack, and so forth. This was done because one system of developing spelling skill is to present words with the same word ending as a group, so students could learn the word ending and then substitute begining letters and consonents. This technique also allows students to learn rhyming words, even though there are exceptions (ahead, knead) and that some words have multiple pronounciations (read).
In field testing of Word Families, handwriting practice was included as SMART Table activity, using the SMART Notebook add-on and Paint activity modules. Special pages were created so that four students could handwrite at the SMART Table at the same time. Although the field testing showed conclusively that students initially liked the freeform ability to write, students finished at different times and then quickly began doodling. This was a natural, but disruptive, behavior. In field testing, it was impossible to keep children on the task of handwriting, and students who didn't finish their own handwriting work couldn't resist doodling like their colleagues were going. Therefore, handwriting practice was removed from the Word Families Activity Packs.