The most common and most likely answer to this crossword clue is the 9 letter word SLOWCOACH
S
L
O
W
C
O
A
C
H
More clues leading to the result SLOWCOACH
- Small blue train, one lagging behind
- One teaching a pig, possibly, to catch large snail
- Small blue vehicle certainly not one of the fleet
- Owls, bizarrely, train tortoise or snail?
- Son depressed on train, one crawling along?
- Plodder is to look into innovative cash cow
- WC a school ordered, not a high-speed type
- 2’s down train doesn’t go fast!
- Laggard finally leaves blue train
- One who is sluggish like a small bleak vehicle
Buddy explains!

The straight part
We know that "Plodder" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case plodder = slowcoach.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SLOWCOACH mean?
SLOWCOACH noun- A person, especially a child, who moves slowly.