A key to the Washington Nationals’ success this season has been the pitching, especially that of Stephen Strasburg, above. (Katherine Frey/The Washington Post)

It’s summer and school’s out. But it’s report card time — for the Washington Nationals.

The All-Star break is always a good time to look at how some key players have done in the first part of the baseball season. Remember, Mr. Bowen is a tough grader. If someone has performed at the level of an average major leaguer, he gets a C, even though an average player can help a team.

Let’s take a look at the Nats, the first-place team in the National League East with a record of 54 wins and 36 losses.

Starting pitchers

Gio Gonzalez: D

Tanner Roark: B+

Joe Ross: B

Max Scherzer: B+

Stephen Strasburg: A

The key to the Nats’ early success is that they have the best pitching in the major leagues. The top three starting pitchers — Scherzer, Strasburg and the underrated Roark — have been terrific. Strasburg has been amazing, with a perfect 12-0 (12 wins, no losses) record.

Ross has been a pleasant surprise for a 23-year-old. I love Gonzalez, but he is the weak link on this very strong staff.

Infield

Danny Espinosa: B

Daniel Murphy: A

Wilson Ramos: A

Anthony Rendon: C+

Ryan Zimmerman: D+

Murphy has been the team’s most valuable player and maybe the MVP for the entire National League. He is leading the majors in batting average with a .348 mark. Ramos has been almost as good, a true All-Star at catcher.

Espinosa is blossoming into a dependable everyday shortstop with surprising power (18 home runs). Rendon has been okay, but Washington fans are still waiting for him to get hot at the plate.

I’m not happy about giving Zimmerman such a low mark. But he deserves it. After so many injuries, Zimmerman looks old for a 31-year-old ballplayer.

Outfield

Bryce Harper: B+

Ben Revere: D

Michael Taylor: D+

Jayson Werth: C

Harper may not be playing like the MVP of the 2015 season, but he is still very good. After a slow start, Werth is hitting better and contributing.

I wonder how good the Nats could be if either Revere or Taylor started playing better in center field and at the top of the batting order. Maybe we will find out in the second half of the season.

Outlook

Manager Dusty Baker (B+) has done a wonderful job handling the bullpen (B+) and giving the players on his bench (B) an opportunity to help out. He’s a leader.

Keep your fingers (and toes) crossed. If the Nats can stay healthy, Baker may lead them all the way to the World Series.

Bowen writes the sports opinion column for KidsPost. He is the author of 21 sports books for kids, including nine baseball books.