Yes, agreement is necessary, but according to the rules, which means that the place of the object determines whether aggreement is made or not.

• Quelle route a-t-elle prise ? but Elle a pris quelle route ?
• Quelle voiture a-t-il choisie ? but Il a choisi quelle voiture ?
• Quelles cérémonies a-t-il vues ? but Il a vu quelles cérémonies ?

You must write “Quels progrès ont faits ces étudiants ?”.

Addition suggested by the comments, in particular that of user dralpuop (somewhat off topic but there is no other way to provide the beginning of a follow-up to the questions raised; to be read only if desirous to delve further into the ideas put forward in the comments.)
“Quels progrès ont faits ces étudiants ?” sounds nice. Other forms are intricate and unpleasant to hear.

Addition

It is very subjective. In English, where a unique consistent form is used for questions and where subject/verb inversion is the mark of a question there is no possibility of saying “What progres those students made?” (“What progres made those students?” is the only correct form); in French it is not different: the mark of such questions is the inversion; in this latter language a question form where the inversion is not used is tolerated but it is deemed to be very colloquial and can’t be used in text or serious talking, presumably because it is unsystematic.

In English, if the subject is a pronoun you can’t use inversion if an auxiliary is not used in the verb form and you have to introduce an auxiliary (What progres did they make?) which restitutes the inversion (This is “do”.). (“What progres made they?” is just not correct.) It is the same thing in French except that instead of introducing a special supplementary contraption in the syntax to palliate to a subject pronoun form that has been found defective on the count of usage (…made they…) you do that for a subject noun form that is defective on the count of systematics (…ces étudiants ont faits…).

French remains consistent and simple as far as the treatment for the pronoun and the noun are essentially the same; in both languages the pronoun must appear right after the auxiliary, whether it is an added auxiliary or one that comes initially with the verb form.

Of course you do have “Quel progrès ils ont faits ?/What progres they made?” but that is colloquial in French and simply incorrect in English because it is a form that does not respect the subject verb inversion for such questions.

As in English (instead of an auxiliary that manages an inversion form, a “pronom de rappel” introduces this inversion in French) there is only a restitution of an inversion in “Quels progrès ces étudiants ont-ils faits ?”. Why should the English “What progres did they make?” sound neither intricate nor unpleasant while the French parallel construction “Quels progrès ces étudiants ont-ils faits ?” would do so?

The impression is therefore quite subjective, probably induced by the common occurrence of the colloquial “Quel progrès ces étudiants ont faits ?” and “Quels progrès ils ont faits ?” which is in opposition to the formalism of “Quels progrès ont-ils faits ?” and “Quels progrès ces étudiants ont-ils faits ?”.

Let’s note one of the positive points in the use of this pronoun (called either “pronom de rappel” or “pronom de reprise”) as formulated in LBU.

Observations générales sur l’inversion du sujet.
Des interrogations comme « Quel patron préfère Durand ? » « Qui aime Jean ? »
sont ambiguës, car « Durand » et « Jean » comme « quel patron » et « qui » peuvent être objets directs ou sujets. Il est préférable de choisir des tours plus nets : « Qui Jean aime-t-il ? », « Qui est-ce qui aime Jean ? » etc.

Ex. plus ou moins ambigus

• Quel appui cherchait son front . (MAURIAC, Fleuve de feu, IV.)
• Quelles alliances concluront nos entreprises avec des firmes
  étrangères . (Raym . ARON , d ans l’Express, 27 aoû t 1982.)
• Quels prêtres pourront bien faire ces romantiques en ébullition . (GREEN, Vers l’invisible, p. 388.)
• Quelle procédure d’observation permit la théorie de la grammaire comparée . (G. BERGOUNIOUX, dans Langue fr., sept. 1984, p. 9.)

Il y a des cas où le sens de la phrase indique nettement quel est le sujet et
quel est l’objet.

• Quel âge a mon oncle ? (PROUST, Les plaisirs et les jours, p. 21.)
• Quel crime a commis sa mère ? (ÉLUARD, Nécessités de la vie, Montre avec décors.)