The Tools for Training Handwriting program makes use of different sized grids and single lines for teaching the motor plan and the positioning and sizing of letters.
Very large block templates
An A4 writing surface divided into four blocks is about the right size for introducing a new letter. This provides a big enough space for writing a large letter using shoulder / elbow movements with a steady wrist.

Large block template
Once the strokes or sequence of strokes that make up a letter have been learned, the letter is practised in a grid of large blocks (6 X 8 cm).
The size of the blocks is still large enough to ensure that the learner uses shoulder / elbow movements rather than finger movements to write the letter.
A printed grid inserted into a plastic sleeve or laminated is a good option for providing a writing surface that can be reused.
Small blocks in a single line grid
Once the learners have learned the motor plan for the letters, move on the writing the letters in a small block single line grid to encourage the learners to write the letters using finger actions.
The base line of the grid is thicker to remind the learners to write the letters so that they rest on the base line.
The emphasis is on writing the letters so that they are fairly well formed and are of a size that fits into the blocks.
Single lines
As soon as the learners have a good idea of how to write a few letters and are able to write these letters in a small grid, they need to start combining letters to form words and learn to write the letters on a single line.
The single line helps with the positioning of the letters in a straight line without imposing strict size requirements. The emphasis remains on writing a fluent, preplanned letter with minimum need for visual monitoring as the letter is being written. With practice the learners learn to adjust the writing movements to produce letters of more or less the same size.
Writing letters on a single line means that the learners need to make a judgment about the start position for the next letter and have to plan the movement of the pencil tip through the air (ie off the writing surface) as it is moved to the start position for the new letter. It takes practice before this in-air action is fluent and can be done without visual monitoring.
Once learners start to write words they also need to start practising leaving a space between words. This is best introduced by emphasising the need to move the hand to the left before starting to write the new word. Once the hand is repositioned and the new start position is located visually. This allows the child to plan the movement of the pencil tip in the air to the new start position.
Writing lines with soft edges to guide letter size
Double writing lines with soft edges is another option when learners are just starting to write words. The top and bottom lines are broad light grey lines and learners are encouraged to form letters so that the top and bottom of the letter lies within this area.
This option is particularly useful for learners who have difficulties with sizing letters without some visual guidance.