Steelers coach Mike Tomlin and quarterback Ben Roethlisberger struggled to produce enough offense this season. (US Presswire)

The Steelers finished 8-8 after a 6-3 start, so their final grades aren’t going to be pretty after that final semester’s work. It wasn’t a case of senioritis, although a few of the more senior Steelers players may get dumped so the club can both infuse the roster with youth and delete some $10 million-plus in salary cap overage.

True, injuries undermined an already thin lineup, with players considered regulars or starters missing a sum total of 60 games this season. But the standard of play dropped precipitously in the final half of the season, with that 2-5 finish.

Offense: D

In that 6-3 start, this unit was on its A game -- A-minus at worst. Then it went kaput. Pittsburgh topped the NFL with a 50.4 third-down conversion percentage in the opening half of the season, then in the final seven games compiled a 37.1 percentage. Ben Roethlisberger completed 67.1 percent of his passes and averaged 275 yards per game in the opening half of the season, then completed 54.5 percent for 212 yards per game after coming back from his shoulder injury. By any statistic, that’s a huge dropoff. Worse, Roethlisberger threw the ball to the other side too often: four of his eight interceptions came in the final four games, leading to 13 of the final 26 points scored by opponents. Yeah, he was a big reason in the offensive downfall. Yet he got little help from Mike Wallace with drops and less than his usual level of play, a three-game absence by Antonio Brown and an unsettled running game which a surprising Jonathan Dwyer topped with the fewest rushing yards by the Steelers’ leader (623) since 1991.

Defense: A-

How can the NFL’s No. 1 defense in total yards and passing yards and No. 2 in rushing yards -- barely missing the triple crown -- earn anything below an A+? The honest way, that’s how. Defensive coordinator Dick LeBeau’s unit did blow games early, allowing Oakland and Tennessee to not only score 60 points between them, but win those games in the fourth quarter. Then it got better ... appreciably better. After allowing 23 points on average the opening five games, LeBeau’s Pittsburgh defense permitted 18 the rest of the way. Five of their final 10 foes scored 13 points or fewer. All this from a unit that didn’t live by the sack or the turnover, with just 10 interceptions -- the franchise’s fewest in a 14- or 16-game season.

Special teams: C

Mike Tomlin fired special teams coach Al Everest in the preseason, and things didn’t get much better. Penalties abounded, erasing good returns. Not one but two fake-punt runs by opponents in the final four weeks went for first downs and critical yardage. Tomlin benched special-teamers who were “egregious offenders,” symbolically making them inactive -- “taking away their helmet,” was how he put it. Rookie punter Drew Butler and rookie returner Chris Rainey showed promise for the future.

Coaching: C

Tomlin took the Steelers to the Super Bowl in two of his first four seasons, a pretty impressive percentage. But the past two seasons saw a one-and-done in the playoffs, then this disappointing year in which Pittsburgh lost five of eight games decided by a touchdown or less and dropped four games against teams with no more than four victories at the time (Oakland, Tennessee, Cleveland and San Diego). He lost his respected offensive line coach, Sean Kuglar, to the Texas-El Paso head coaching job and also needs to find a special teams coach. A staff once marked by its stability is getting, much like the roster, something of a facelift.

Cumulative GPA: 2.175 

Follow Steelers reporter Chuck Finder on Twitter @CBSSteelers and @cfinder.