It's an option that would mean schools can choose to bring in groups of new entrants together at the beginning of the term, rather than having them show up piecemeal throughout the year by themselves.
Don't forget, children in this country aren't required by law to attend school until they turn 6.
If a parent is concerned that their 4-year, 44-week-old child isn't ready to start school, they're perfectly entitled to wait out those extra eight weeks, or even longer if it's in the best interests of the child.
This kind of flexibility is a great thing for young children; it allows them all to move at the pace that's best for them.