Lobularia maritima - Sweet Alyssum
I have fond memories of Sweet Alyssum from the garden of my paternal grandmother (one of the first gardens I recall in detail). The form she grew was very tall, very fragrant, with white flowers that faded to lavender, creating a two-tone effect in each flower head.
This particular planting (at a local school, created under my assistance) seemed to exhibit individual plants of similar type from time to time as the plants self-seeded around the bed in quantity. I had hoped to find an example of that on this day but they seemed to have been best loved by little children's hands seeking presents for teacher or parent.