John Lees’s review published on Letterboxd :
X+Y plays a bit like a sports movie where athletes have to overcome the odds to succeed, only instead of sports its maths and instead of athletes its socially awkward teenagers with autism. The contest in question here is the International Maths Olympiad, a real-life event which director Morgan Matthews previously made a documentary about. This film is a fictionalised partial adaptation of that documentary, telling the story of Asa Butterfield's Nathan, a painfully shy autistic boy with autism, who is forced out of his withdrawn world when his brilliant mathematical mind sees him added to the British maths team for the IMO and sent off to train in Taiwan.
The film starts off a bit clunky, with some heavy-handed music cues and predictable plot beats, and the boy playing young Nathan isn't too great. But things really pick up when we fast forward in time to Nathan as a teenager, played brilliantly by Asa Butterfield. Asa first got himself on my radar as a young actor of note with his lead role in Martin Scorsese's HUGO, and here he builds on that reputation with an incredible performance. Neville's struggle with situations and emotions he's not quite able to understand is really touching viewing, and there are moments that will bring you close to tears. It's astounding work, great enough to be put up there with some of the better adult performances of the past year.
He's ably supported by a gifted ensemble around him. Sally Hawkins is heartbreaking as Nathan's struggling mother, the pain palpable in her eyes when Nathan apparently doesn't return her immense love for him. Rafe Spall is also fantastic as Nathan's maths tutor, a source of humor in the film but also someone struggling with his own demons and afflictions. I honestly didn't rate Rafe Spall as more than a comedic actor before this, but here he shows he really does have the chops. And the always-reliable Eddie Marsan is on hand to provide some comic relief as the oddball IMO UK team leader.
X+Y has a couple of elements holding it back, such as the aforementioned ropey opening and the heavy-handed presence of "inspirational ghost dad" who comes back to telegraph to us our characters' feelings in sepia-toned flashbacks. But there really is a lot to love here, leaving you emotionally invested in some unconventional romances, and swelling your heart at the small triumphs of the human spirit. And who knew maths could be so exciting?