The 19-year-old has become one of David Moyes’s most trusted players this season, starting every Premier League match as he establishes himself in the senior side.
For a player who has come through Everton’s academy, the experience of lining up alongside established names has brought some unusual moments. Grealish is a particularly striking example, having been a player Armstrong watched from home before the pair became team-mates.
“There are moments where you’re coming up against players who I’ve watched since I was young,” Armstrong said.
“Even playing with players. Not that long ago, I was sat on the couch at home watching Jack (Grealish) in the Champions League.
“To say they’re my teammates now is surreal, really. But I think it’s a feeling you’ve got to manage at times – managing the balance of respecting them, but also proving yourself and showing what you’re capable of.”
Armstrong’s rise has been rapid. He was close to leaving Everton for Nottingham Forest during the summer transfer window, but the proposed move was abandoned following a strong reaction from supporters.
Instead, he has remained at the club he joined as a young child and taken his opportunity in Moyes’s team. The midfielder is pleased with his progress but is already looking for ways to make a greater impact.
“There’s definitely things I can improve on,” he said. “I’m happy with where I’m at, but I definitely want to push on.
“I want to improve on goals and assists and influencing games more. I know from playing football since I was young and being here since the age of four or five, I’ve seen different parts of my game and how I can draw it out more.
“To do that in the best league in the world is difficult, and at times, you’ve got to respect that you’re playing with some of the best players in the world and coming against some of the best opposition.
“But I think there are definitely more levels for me to go to. To do that, I have to do the basics well, but also be myself, take risks and not be too bothered about not getting it right every time.”
The midfielder credits Moyes with giving him the confidence to develop, pointing to the manager’s decision to select him consistently as evidence of the trust placed in him.
“He gives 100 per cent trust in me. I think the fact I’ve started every Premier League game this season shows that,” Armstrong said.
“He’s someone who has been in the game a long time and has worked with some of the best English players to have come through.
“To have someone like that with so much experience and so much to learn from is really important. The trust he’s shown in me, I’m really grateful for.”
That support does not mean the manager allows him to become complacent. Armstrong says Moyes is demanding and regularly challenges his assessment of his own performances.
“Yeah, really demanding. I think sometimes I’ll come off and I think I’ve played better than what he thinks! But it’s a good relationship.
“He knows how to get the best out of me, how to push me. Hopefully, we can do really good things. Sometimes that’s what you need, isn’t it? To keep your feet on the ground and I understand what you need to do to improve.
“I think that’s almost part of Everton’s DNA – not getting too high and not getting too low. I think it’s a club that’s very demanding of hard work and staying grounded – and he definitely applies that.”