The 14 year old boy, who cannot be named because of his age, admitted a charge of possessing an offensive weapon but denies murder.
He appeared at Liverpool Crown Court on Friday.
Ava, 12, was fatally stabbed in the neck near Church Alley following the event on 25 November.
The suspect appeared via videolink at Liverpool Crown Court on Friday charged with her murder.
About a dozen members of Ava’s family were in court for the hearing, which lasted about half an hour, and some were in tears as the teenager entered his pleas.
Judge Mrs Justice Yip told the defendant: “Your trial is going to take place in May, starting 9 May.”
The case is expected to last three weeks.
Ava, who has been described as “popular” and “bright”, was assaulted in the city centre just after 8.30pm.
She was taken to Alder Hey Children’s Hospital after paramedics arrived, but died a short time later.
After her death, her father, Robert Martin, said the family were “completely devastated and heartbroken”.
Three other boys were also arrested following Ava’s death.
A Merseyside Police spokesman said a 16-year-old boy was released on bail, a 14-year-old was released under investigation and no further action was taken against a 13-year-old.