The phrase "become a milestone" is grammatically correct and commonly used in written English.
It is typically used to describe a significant event or accomplishment that marks a major change or achievement. Example: The discovery of penicillin became a milestone in the history of medicine, revolutionizing the treatment of infections.
Yet there he was, with his classmates at Creative Beginnings Children's Center, about to celebrate what has become a milestone in this season of commencements: the preschool graduation.
They hope to perfect a procedure they claim "will become a milestone of medical history and potentially could save millions of people".
As the music business continues to shift from an emphasis on recorded-product sales and toward live performances and other kinds of direct engagement with fans, a successful festival of one's own has become a milestone for the sort of bands that don't play the same set list night after night.
The improvement of hydraulic support model has become a milestone of longwall mining technology development and a decisive factor of mining technology innovation.
With these major developments, 2015 could possibly become a milestone in the history of light art, with the Unna museum serving as a creative epicenter for the field. .
Agreement on the nuclear issue has the potential to become a milestone on the road to regional security, and would encourage Iran to open itself to the world further.
On 2 October, two dozen AIDS researchers gathered to learn whether an HIV prevention study they had just completed would become a millstone or a milestone for the field.
Its conclusion became a milestone in epidemiology: Smokers had a marked increase in lung cancer risk.
In the early 1970s, Dr. Harper provided the creative spark for a project that became a milestone in women's art.
Still, the Snow Brand case became a milestone in Japan, helping open the floodgates for a series of similar scandals.
With AIDS, the clear need for drugs outstripped the naysaying, and the success of the anti-H.I.V. drugs became a milestone in antiviral treatment.
