Keon Lincoln, 15, died in hospital after he was fatally shot and stabbed as he left his front door on Linwood Road, Handsworth just after 3.30pm on January 21.
Witnesses said shots were heard and the suspects were armed with knives. Officers believe the group fled in a white car, which later crashed into a house in Wheeler Street, Lozells.
Keon was taken to hospital but later died.
West Midlands Police said a 14-year-old boy was arrested at his home address in Birmingham on Saturday night and two others, aged 15 and 16, were arrested at an address in Walsall in the early hours of Sunday.
All three were detained on suspicion of murder and will be questioned by police.
A 14-year-old boy arrested on Friday evening has been released under investigation, and detectives have been granted more time to question another 14 year-old arrested on Friday morning.
Detective Chief Inspector Alastair Orencas, leading the investigation, said: “There has been no let-up in our quest to find those responsible for Keon’s murder and these are significant arrests.
“We are gathering a substantial amount of evidence which will take time to analyse, but we must be thorough to get justice for Keon’s family.
“They have been fully updated with the latest developments.”
Neighbours told the Sun that Keon's mother, who works as a cleaner at a local school and has four other kids, were devastated by the tragedy.
Earlier this week, Keon’s family family paid tribute to him, saying, "It is with profound grief that we announce the passing of our beloved Keon, who was senselessly taken from us on Thursday 21st January.
“Keon was a fun loving 15-year-old who was full of life and love for his family and friends. He had an infectious laugh that lit up the room whenever he was in it.”
Police continue to urge anyone with dashcam footage or any other information related to the case to come forward.
The force can be contacted via Live Chat on its website or by calling 101. Information can be given via our dedicated portal on https://mipp.police.uk/operation/20HQ20H42-PO1 or anonymously to Crimestoppers on 0800 555 111.