There's actually been serious research into which approach is more effective.
The biggest study of this was done in the UK. Researchers there concluded that synthetic phonics (building up words from their constituent sounds) is more effective than analytic phonics (the “whole word” approach) after finding that:
- After 1 year, students taught with synthetic phonics had reading ability approx. 1 year ahead of their chronological age (i.e., ahead of the reading ability of students taught with analytic phonics), and also had spelling ability that was at least 1 year ahead of the spelling ability of students taught with analytic phonics.
- The advantage demonstrated by students taught with synthetic phonics is persistent, rather than temporary. In subsequent years, the synthetic phonics students continue to have a lead of at least 1 year, in both reading and spelling, over students taught with analytic phonics.
- Groups of disadvantaged children, who have historically underachieved when taught with analytic phonics, did not underachieve when taught with synthetic phonics. This was consistent with the observation made by some researchers that, although there tends to be a “tail” group of students who significantly underperform with analytic phonics instruction (whether they belong to a “disadvantaged” group or not), the use of synthetic phonics almost entirely eliminates this “tail.”
Researchers believe that the reasons why synthetic phonics is more effective are:
- Knowledge of letter sounds (or phonemes), or even just letter names, has been found to be the strongest predictor of reading achievement. Synthetic phonics teaches letter sounds early in the instruction process.
- Blending together individual sounds has been found to be a strong predictor of reading achievement (when measured before the beginning of formal instruction). Synthetic phonics explicitly teaches blending skills.
- Segmenting words into sounds has been found to be a strong predictor of spelling ability. Synthetic phonics explicitly teaches word segmentation.
- The synthetic phonics approach engages the left brain (as shown by MRI studies), rather than the right brain, which is engaged by the analytic phonics approach. The left brain is more efficient at processing language.
- There is a theory for why synthetic phonics should work better: the use of letter sounds, blending and segmenting reduces the cognitive load on the student. Here's what this means, as I understand it. When trying to identify short words, there are relatively few possible solutions to consider, but the number of possible long words is enormous. The number of possible solutions grows exponentially with the length of the word, so that the analytic phonics student, in trying to identify the whole word directly, quickly faces a problem of tremendous complexity. In contrast, identification of the individual sounds in the word, followed by blending them together, presents the student with a problem that grows only in proportion to the length of the word. Beyond short words, this gives a huge advantage to the synthetic phonics student.