There's more to Interlock than you might have been told!
I used the Weaver Interlock with five children.
I read the description above and found it to be confusing, or possibly simply lacking.
Let's be more specific.
Math concepts covered in preschool include shapes and numeral identification. Kindergarten concepts include the counting, order, and comparisons of numerals 0-100. If your K child needs more than early addition, then you will need to find a first grade math program which begins with K review and moves on to higher concepts. To say that math is not included could confuse people, but I have read this in several critiques.
Phonics is not included because children are ready to read at different times. Imagine the chaos that would ensue if you were constantly having to rewrite lesson plans for a phonics-based program when your child was beyond or not yet at that level? Wisely, the author kept phonics separate. She wrote a complimentary multi-sensory phonics program called 123READ! if you want to do phonics lessons with your child. 123READ! has three levels which are not connected with the lesson plans in the Weaver Interlock. This allows you to begin phonics studies when and where you need to start without having to skip back and forth in the Interlock manual.
I view the simplicity of the math and the separation of phonics as pros, not cons to the value and usefulness of the Interlock!