The Baggies are lying in sixth spot in the Barclays Premier League after 19 games, having collected 33 points ahead of Saturday's clash away to leaders Manchester United. There were question marks over Clarke's appointment - his first in a senior role after being number two at Newcastle, West Ham, Chelsea and Liverpool.
However, assistant-boss Downing said: "I think we've surprised a few people. I don't think we've surprised ourselves. It's been a work in progress the last two or three years. The club has worked exceptionally hard behind the scenes."
Downing added: "The players have been collected and there has been a real strengthening of the squad. It's been built up over the years. I don't think it has surprised us from within. Thirty-three points at the half-way stage is a fantastic return for a club like us.
"We have to reset the goals. We are still looking at 40 points and people will raise eyebrows at that, but that's our prime objective, to stay up for another season. Then we can assess things again once we get to 40 points but we are not jumping ahead of ourselves and we've got a lot of people with their feet on the ground."
Clarke has adhered to the 'if it isn't broke, don't fix it' approach in not making wholesale changes although he has brought a more attack-minded approach to the squad.
Downing said: "We felt quietly confident at the start that we would have a reasonable season and the biggest worry is maybe the fact there was a change of manager. But Steve has come in and it's been seamless. There were big shoes to fill after Roy (Hodgson) but Steve has done exceptionally well in his first job as a manager.
"People doubted his first job as a manager but he has been very good. His strength is that he has realised what the strengths of the club were, and what Roy did, and he has put his own slant on things without revolutionising anything. That has been the strength of Steve."
Downing is hoping Albion can cause United the kind of problems defensively that Sir Alex Ferguson admits are a cause for concern. He said: "I think you are looking at their strengths and weaknesses and Sir Alex has mentioned there is a cause for concern with the goals they have conceded.
"But they have top quality players. (Nemanja) Vidic is coming back and in (Chris) Smalling and (Phil) Jones, they have a lot of individual quality there. I'm sure that is something they will be working on but there is an opportunity to go there, particularly after the two wins, with a freedom to our game and hopefully we can give them a few problems."