Solution to 25D has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
ACROSS
1 0-9 students hate to score (6-5) SINGLE-DIGIT [DD]
9 Implicate doctor in emergency room operation incident lapse primarily (7) EMBROIL {E{MB}R}{Op...n}{In...t}{La..e}
10 The body part that can turn either way (7) ROTATOR <=> [C&DD]
11 Bank rate eclipsed distress recovery sign (5) LIBRA {LI{BR}A<=}
12 Offer to look back into risky venture (9) VOLUNTEER {V{LO<=}UNTEER*}
13 Reviewing puzzle without answer? Write differently (5) RESET TEaSER<=
15 Variety of rebates on food (5,4) ROAST BEEF*
18 They decide the winners by draw in split second (3-6) TIE-BREAKS {TIE}{BREAK}{S}
21 Side dish served up in party in air regularly (5) RAITA {pArTy+In+AiR}<=
22 180°! (5,4) VOLTE FACE [CD]
24 Unhappy man leaves mortal to become ascetic (5) SADHU {SAD}{HUman}
26
Duettos composed in
shelter (7)
TESTUDO*
27 Oddly
st
up
id
ch
il
dr
en
end it all (7)
SUICIDE {S
tU
pI
d+C
hI
lD
rE
n}
28 Lodger staying up with girl friends essentially in disguise (6,5) PAYING GUEST {STAYING+UP+G+friEnds}*
DOWN
1 Have doubts about returning sailor with all birds leaving skuas heartily (5,1,3) SMELL A RAT {TAR}{ALL}{EMuS}<=
2 Celebrity almost grabs honour (5) NABOB {NABs}{OBe}
3 Floater at sea sheltered very good nurse (4,5) LOOK AFTER {LO{OK}AFTER*}
4 Daughter given sedative finally on the organ to give birth (7) DELIVER {D}{s...vE}{LIVER}
5 African native, good or bad associate? (7) GORILLA {G}{OR}{ILL}{A}
6 Giant stretch, I hear (5) TITAN (~tighten)
7 Alien broadcast endless secrets of one and all other people? (2,6) ETCETERI {ET}{SECRETs*}{1}
8 You say this when freezing bishop comes with many rooks (4) BRRR {B}{RRR}
14 Unwanted switch of poles gets grape variety (8) SEEDLESS (-n+s)SEEDLESS
16 Dreadful night to admit impulsive defeat (9) THRASHING {TH{RASH}ING*}
17 Windy apartment gets upper-class lease housing central banks (9) FLATULENT {FLAT}{U}{LE{baNks}T}
19 Incorporate small particle in some detailed analysis (7) ANATOMY {AN{ATOM}Y}
20 Some say — no, let it stand over headgear (7) STETSON {Say}<=>{NO{STET}<=
22 Reject franchise cycling backwards (4) VETO (-v}OTE(+v)V<=
23 Supply drug to queen in person at first (5) EQUIP {E}{QU}{In}{Pe...n}
25 Liquefy bomb, diffuse valency basically (2-3) D?-I?E (Addendum - DE-ICE DEvICE - See comments)
Reference List
Emergency Room = ER, Look = LO, Answer = A, Second = S, Girl = G, Daughter = D, Good = G, Associate = A, Alien = ET, Bishop = B, Rook = R, Upper-class = U, Drug = E, Queen = QU, Valence = V